Automatic transmission

Abstract

Forward nine speed stages are achieved by four planetary gear units and six frictional elements and established by combination of synchronously fastening three of the six frictional elements. To an automatic transmission having the above-mentioned units and elements, there are added a first connecting member (M 1 ) that connects a first ring gear (R 1 ) of the first planetary gear unit (PG 1 ) to a second carrier (C 2 ) of the second planetary gear unit (PG 2 ) and, a fourth brake (B 4 ) that is able to fix the first connecting member (M 1 ) to a transmission case (TC). By combination of simultaneously fastening three of the seven frictional elements with fastening of the fourth brake, at least one new speed stage is established so that the automatic transmission establishes forward speed stages that are equal to or more than forward ten speed stages.

1 . An automatic transmission comprising:
 a first planetary gear unit, a second planetary gear unit, a third planetary gear unit and a fourth planetary gear unit which are employed as four planetary gear units;   a first brake, a second brake, a third brake, a first clutch, a second clutch and a third clutch which are employed as six frictional elements, the automatic transmission establishing forward nine speed stages by combination of simultaneously fastening three of the six frictional elements,   wherein:   a fourth brake is added to the six frictional elements thereby to provide seven frictional elements, the fourth brake detachably fixing a connecting member to a transmission case, the connecting member connecting a first ring gear of the first planetary gear unit to a second carrier of the second planetary gear unit; and   at least one speed stage is added to the automatic transmission by combination of simultaneously fastening three of the seven frictional elements with fastening of the fourth brake, so that the automatic transmission establishes speed stages that are equal to or more than forward ten speed stages.   
     
     
         2 . An automatic transmission as claimed in  claim 1 , in which:
 a first speed stage is established when the second brake, the third clutch and the fourth brake are simultaneously fastened;   a second speed stage is established when the second brake, the third brake and the third clutch are simultaneously fastened;   a third speed stage is established when the second brake, the second clutch and third clutch are simultaneously fastened;   a fourth speed stage is established when the second brake, the third brake and the second clutch are simultaneously fastened;   a fifth speed stage is established when the second brake, the third brake and the first clutch are simultaneously fastened;   a sixth speed stage is established when the third brake, the first clutch and the second clutch are simultaneously fastened;   a seventh speed stage is established when the first clutch, the second clutch and the third clutch are simultaneously fastened;   an eighth speed stage is established when the third brake, the first clutch and the third clutch are simultaneously fastened;   a ninth speed stage is established when the first clutch, the third clutch and the fourth brake are simultaneously fastened;   a tenth speed stage is established when the first brake, the first clutch and the third clutch are simultaneously fastened; and   an eleventh speed stage is established when the first brake, the third brake and the first clutch are simultaneously fastened, so that the automatic transmission establishes forward eleven speed stages,   wherein the first speed stage added due to fastening of the fourth brake is set to a super-low gear ratio speed stage that is further lower in gear ratio than the first speed stage of the forward nine speed automatic transmission; and   wherein the ninth speed stage added due to fastening of the fourth brake is set to a high gear ratio speed stage that has a gear ratio put between respective gear ratios of the seventh and eighth speed stages of the forward nine speed automatic transmission.   
     
     
         3 . An automatic transmission as claimed in  claim 1 , in which:
 the connecting member is a cylindrical drum member that is arranged to cover outer peripheral sides of the first and second planetary gear units; and   the fourth brake is disposed between an outer peripheral surface of the connecting member and an inner peripheral surface of the transmission case that faces the outer peripheral surface of the connecting member.   
     
     
         4 . An automatic transmission as claimed in  claim 3 , in which:
 the fourth brake is a multiple disc brake that comprises mutually sandwiched drive and driven plates;   the connecting member is formed at the outer peripheral surface thereof with spline-engagement grooves with which the drive plates are engaged; and   the transmission case is formed at the inner peripheral surface thereof with spline-engagement grooves with which the driven plates are engaged.